The Gatekeepers must be seen, by anyone who seeks better understanding about seemingly intractable tensions between Israelis and Palestinians.

A documentary on the former leaders of Shin Bet, Israel’s internal security agency. Directed by Dror Moreh. 97 minutes. Opens March 1 at the Varsity. 14A

A monolith crumbles in The Gatekeepers, and it’s a sight to inspire awe.

Israeli documentarian Dror Moreh takes us inside the Shin Bet, his country’s internal security and anti-terrorism service. He shines a spotlight not just on this shadowy operation — its motto is “The Unseen Shield” — but also on the conflicted intentions and mixed emotions of the men who run it.

Contrary to the usual “no comment” stance of spy agencies, these men offer with unprecedented candour their strong opinions on why Israel has been unable to secure a lasting peace with Palestinians. They blame a series of missed opportunities and tragic missteps on both sides of the conflict, dating back to Israel’s territorial expansion following the Six-Day War of 1967.

It is not overstating the case to say that this is a film that must be seen, by anyone who seeks better understanding about seemingly intractable tensions between Jews and Arabs in the Middle East. A hit at TIFF last year, The Gatekeepers was among the nominees for Best Documentary Feature at the recent Academy Awards. It should have won.

Moreh manages to get on camera all six surviving former Shin Bet leaders, beginning with the most recent one, Yuval Diskin, who directed the agency from 2005 to 2011. He introduces the film’s theme of the “different shades of grey” that increasingly make it hard to tell the good guys from the bad ones and that make peace seem a faint hope for both Israelis and Arabs.

All dressed casually — Shalom looks grandfatherly in his wire specs and suspenders — these men might in other circumstances be taken for a group of like-minded friends discussing current affairs.

But they aren’t pacifists. There’s no mistaking their serious intent, their loyalty to Israel or their willingness to use advanced surveillance and primitive violence — including various forms of intimidation on imprisoned terror suspects — in order to protect their country.

In one of Moreh’s chilling recreations of Shin Bet operations, set to an electronic score that seems taken from science fiction, we watch as a cell phone packed with explosives is used to blow the head off a high-ranking terrorist.

Yet, to a man, all of these former Shin Bet leaders express serious misgivings about the direction their country is headed. They lament that nothing has replaced the hopefulness of the 1993-94 Oslo Peace Accord, a two-state solution that broke down in 2000 following a wave of social and political unrest, which included the 1995 assassination of Israeli Prime Minister Yitzhak Rabin, killed by a radical Jew who objected to any accommodation with Arabs.

Rabin’s assassination happened on Gillon’s watch, and his regret at being unable to protect his national leader can be seen in his eyes and in every line of his haggard face. But he speaks with pride of how the Shin Bet successfully foiled an attempt by the Jewish Underground to blow up the golden Dome of the Rock on Temple Mount in the Old City of Jerusalem, an act he predicts would have sparked a “war of Armageddon” by enraged Muslims.

Some of the bungled efforts made to cross the Israeli-Arab divide would be almost comical, if the situation weren’t so grave. Dichter tells of how as a young man, while participating in a census of the many Arabs who came under Israeli occupation following the Six-Day War, he inadvertently ran into a linguistic nightmare: the phrase “We came to count you” came across as “We came to castrate you” to Arab ears.

Perhaps most worrisome of all to these men is the increasing number of Israeli settlements on land claimed by Palestinians, a situation they view as anathema to any peace hopes.

Ayalon sums up their common sentiment regarding the current standoff between Israelis and Arabs: “We wanted security and got more terrorism. They wanted a state and got more settlements.”

The Gatekeepers doesn’t pretend to have all the answers. It shows how mistakes have been made on both sides of the conflict, and how difficult it is to discern between right and wrong courses of action in complicated situations.

The film makes for grimly fascinating viewing, but it also inspires a measure of hope. If a monolith this big and men this hard can see the error of using the techniques of war to pursue peace, could a real breakthrough in the Middle East finally be possible?